European Spine Journal 2009 (Nov); 18 (11): 1677–1685 ~ FULL TEXT
Amir Ahmadi, Nader Maroufi, Hamid Behtash, Hajar Zekavat, and Mohamad Parnianpour
Faculty of Rehabilitation,
Iran University of Medical Sciences,
P.O. Box 15875-4391,
The study design is a prospective, case-control. The aim of this study was to develop a reliable measurement technique for the assessment of lumbar spine kinematics using digital video fluoroscopy in a group of patients with low back pain (LBP) and a control group. Lumbar segmental instability (LSI) is one subgroup of nonspecific LBP the diagnosis of which has not been clarified. The diagnosis of LSI has traditionally relied on the use of lateral functional (flexion-extension) radiographs but use of this method has proven unsatisfactory. Fifteen patients with chronic low back pain suspected to have LSI and 15 matched healthy subjects were recruited. Pulsed digital videofluoroscopy was used to investigate kinematics of lumbar motion segments during flexion and extension movements in vivo. Intersegmental linear translation and angular displacement, and pathway of instantaneous center of rotation (PICR) were calculated for each lumbar motion segment. Movement pattern of lumbar spine between two groups and during the full sagittal plane range of motion were analyzed using ANOVA with repeated measures design.
Intersegmental linear translation was significantly higher in patients during both flexion and extension movements at L5-S1 segment (p < 0.05). Arc length of pathway of instantaneous center of rotation (PICR) was significantly higher in patients for L1-L2 and L5-S1 motion segments during extension movement (p < 0.05). This study determined some kinematic differences between two groups during the full range of lumbar spine. Devices, such as digital videofluoroscopy can assist in identifying better criteria for diagnosis of LSI in otherwise nonspecific low back pain patients in hope of providing more specific treatment.
From the FULL TEXT Article:
Low back pain is one of the most common problems in
industrialized countries and its direct and indirect cost is
enormous. Nearly 80% of people over the age of 30 will
experience back problems during some periods of their
life . Eighty five percent of this population is classified
as having ‘nonspecific low back pain’ which contains
little specific therapeutic and diagnostic information and
refers to a large heterogeneous group of patients suffering
from a variety of pathological or pathophysiological
conditions . Despite the increased recognition of lumbar
segmental instability (LSI) as an identifiable subgroup
within this population [3–5], the identification of reliable
and valid clinical diagnostic tools has thus far been elusive
The diagnostic standard for LSI has traditionally
centered on identifying excessive translational or rotational
movements between lumbar vertebrae by using
functional (flexion–extension) radiographs [6–19]. There
may be other factors as well, such as neuromuscular
control of spinal movement and aberrant or abnormal
midrange motion characteristics. Pathway of instantaneous
center of rotation (PICR) may be affected in
presence of segmental instability [20, 21] which has not
been considered in vivo for LSI patients. Therefore, it is
imperative that for assessing some disorders, such as LSI
both quantitative and qualitative characteristics of movement
should be considered.
Traditional radiographic assessment has some limitations,
such as large variation, being based on static postures
at extreme ranges of motion and associated large measurement
errors [7, 22–27]. Therefore, there is a need for
tools to assess kinematics in vivo in order to measure the
motion characteristics in midrange, where aberrant motion
and dysfunction have been postulated to occur, based on
neutral zone concept put forth by Panjabi et al. [28, 29].
Digital video fluoroscopy (DVF) has been suggested as a
tool for reliably evaluating normal and abnormal lumbar
motions in vivo [1, 27, 30–35] and it seems that DVF is
capable of identifying functional abnormalities in patients
with LSI who have no structural abnormalities detectable
by X-ray. Hence, the aim of this study was to develop a
reliable measurement technique that would allow for the
assessment of sagittal plane lumbar spine kinematics using
digital video fluoroscopy in a group of patients diagnosed
having LSI and a control group.
A convenient sample of 15 healthy (12 female and 3 male)
and 15 patients (12 female and 3 male) was recruited.
Healthy subjects were matched with patients (in weight,
height, body mass index, BMI and age) and excluded if
they had experienced LBP 1 year before the study
(Table 1). Patients were examined by a spine surgeon and
diagnosed with LSI according to screening criteria adopted
from Hicks et al.  which requires having at least 3 of 4
positive predictive variables; (1) any aberrant movement
pattern during performance of lumbar range of motion
including instability catch, painful arc of motion and
Gower’s sign, (2) less than 40 years of age, (3) positive
prone instability test at least at one segmental level and (4)
average straight leg raise (SLR) test >90°.
The sensitivity of 0.83 (0.61–0.94) and specificity of 0.56 (0.40–0.71)
were reported for this prediction rule. The prone instability
test is performed in two positions (lying prone with first
resting the feet on the floor and then lifting the legs off the
floor) with posterior pressure applied to the lumbar spine
which is positive when the pain is present in the resting
position but subsides with lifting the legs . Patients were
excluded if their pain was greater than 3 based on visual
analog scale (VAS) during the assessment session. Moreover,
the exclusion criteria for both groups included spine
surgery, spondylolisthesis and a query of pregnancy in
female subjects. All subjects received explanations about
the potential risk of radiation exposure, approved by Iran
University of Medical Sciences and informed consent was
obtained before fluoroscopic investigation.
Pulsed DVF was collected (Fluoroscopy: DAR-300, Shimadzu,
Japan) 5 frame per second and a calibration grid
(2 9 1 cm) was used to calibrate each frame during image
analysis. The maximum radiograph parameters were
50 KV, 47 MA with 12 inches image intensifier and
1 million pixel CCD camera. The images were captured
via a computer directly to random access memory and then
saved directly to a hard disc drive. The average fluoroscopy
time per study was 30 s. A home made software (CARA)
was used to calculate kinematic parameters.
Collection of DVF
As full range of motion was required, subjects were asked
to bend forward from standing at 10° lumbar hyperextension
and then return from full flexion to starting position
(10° lumbar hyperextension). Subjects were instructed to
complete this motion within 10 to 15 s. Sagittal plane was
selected for this study because of greater range of motion
(ROM) and smaller out of plane motion [37, 38]. After
resting and walking for 5 min, subjects were reimaged for
test–retest reliability (interimage reliability). Teyhen et al.
 used a lead harness to improve the quality of the image
and to prevent “white-out” during flexion. In this study,
the special lead harness was designed and placed on the
back of each subject which did not limit their ROM
because of its axis of rotation and could bend freely in
flexion and extension of lumbar spine (Figure 1).
Fluoroscopic intersegmental motion measurements
The sagittal ROM was calculated with reference to the
angle between the projected lines of the lower endplate of
L1 and upper endplate of sacrum as described by Wong
et al.  (Table 1). We measured five evenly distributed
sampling points (0, 25, 50, 75 and 100% of ROM) between
the starting hyperextension position and maximum flexion
(flexion movement arc), and 5 sampling points between
maximum flexion and hyperextension position (extension
movement arc). Each sampling point represents 25% of
either the flexion or extension movement arc. Intersegmental
linear translation and angular displacement in each
sampling point were calculated according to White and
Panjabi method  using customized software.
Instantaneous center of rotation (ICR) was measured for
each lumbar motion segment . Four ICR points were
obtained from 5 sampling images in each movement arc for
each vertebra. Hence, PICR was measured as the total
length of the digital line passing through ICR points.
Interimage reliability was assessed to determine the reliability
of data obtained from two movement trials separated
by a 5 min of rest and intraimage reliability was
assessed to determine the reliability of data obtained from
two separate analyses from 30 randomly selected frames
with 1-month interval by the same observer (AA).
Evaluation of errors
A calibrated board was moved in an arc at varying speed
within the range intended in our experiment while images
were taken by DVF. Since the landmarks on the calibrated
board experienced rigid body rotation in various frames,
the distance and angles between them must have remained
invariant. The root mean square errors were computed from
deviation of measured distances and angles from the reference
(gold standard) values in 30 randomly selected
A Kolmogorov-Smirnov test was performed to determine
normal distribution of each variable. Independent sample t
test was used to test if there was any difference between
two groups for age, weight, height, BMI and sagittal ROM.
The data were coded before analyzing and therefore analyzing
process was blinded.
A mixed between–within subjects analysis of variance
was conducted to assess the effect of phase of movement (5
levels) for each movement arc and each motion segment’s
linear translations and angular displacements. Multiple
comparisons were performed using Bonferroni corrections
between levels of phase of movement. Independent sample
t test was performed to identify the differences of PICR
between two groups. Chi-square test was used to identify
differences between groups and patterns of movements.
Confidence level was set at a B 0.05 for statistical significance.
An interclass correlation coefficients (ICC2,1) and
standard error of measurement (SEM) were calculated to
determine reliability and response stability of each measure,
respectively. All statistical analyses were performed
using SPSS statistical software version 16.0 (SPSS, Chicago,
There was no significant difference in variables, such as
weight, height, age, BMI and sagittal ROM between two
groups (Table 1). In LSI group 14 patients showed instability
catch, 5 showed painful arc, 7 showed Gower sign,
10 showed positive prone instability test (at least at 1
segmental level) and 1 showed SLR[90°.
The average ICC was 0.95 for intersegmental angular
displacement (range 0.89–0.98), 0.92 for intersegmental
linear translation (range 0.89–0.96) and 0.95 for PICR
(range 0.94–0.98). The average SEM was 1.19° (range
0.77–1.45) for intersegmental angular displacement,
0.19 mm (range 0.11–0.22) for intersegmental linear
translation and 5.4 mm (range 2.8–8.16) for PICR.
The average ICC was 0.92 for intersegmental angular
displacement (range 0.84–0.96), 0.92 for intersegmental
linear translation (range 0.85–0.96) and 0.93 for PICR
(range 0.85–0.99). The average SEM was 1.19° (range
0.62–1.97) for intersegmental angular displacement,
0.22 mm (range 0.17–0.28) for intersegmental linear
translation and 7.67 mm (range 2.16–17.35) for PICR.
Evaluation of errors
Figure 5, 6
The root mean square error computed from calibrated
board in the linear translation and angular displacement
were 0.26 mm and 0.41°, respectively.
Assessment of lumbar spinal motion
The mean intersegmental linear translation and angular
displacements of lumbar motion segments for both groups
in each direction of motion is depicted in Figures 2 and 3. The
arc lengths of PICR in both groups in flexion and extension
are presented in Figure 4. Average arc length of PICR for
each vertebra was 53.2 ± 17.4 mm (range 47.5–59.9) for
healthy subjects and 57.8 ± 10.9 mm (range 48.9–75.8)
for patients during flexion movement arc. There was
statistically significant difference for arc length of PICR for
extension movement at L1–L2 and L5–S1 motion segments (p<0.05) (Fig. 4).
The results of ANOVA indicated no significant interaction
between group and phase of movement displacements
(linear and angular) except for L5–S1 linear
translation during extension movement, Wilks
Lambda = 0.50, F(4,20) = 4.83, p<0.007 (Figure 5). The
main effect of phase of movement was significant for all
motion segments in both directions (p<0.0005). Multiple
comparison was significant between all phases of movement
for all motion segments in both directions
(p<0.005). The main effect comparing the two groups
was not significant except at midrange of L5–S1 linear
translation in flexion and extension movements (p<0.05)
(Figures 5, 6).
Motion patterns of both flexion and extension movement
arcs were simultaneous in all healthy subjects, but 6
patients at L5–S1 level showed “delayed-sequence”
movement pattern (Chi-square = 7.5, p<0.01).
Lumbar motion kinematics has been evaluated by a variety
of instruments—from functional radiography [8, 9, 12, 13,
26, 40, 41] to cineradiography [42, 43] and videofluoroscopy
[27, 30–35, 44] — in both normal and patient subjects.
Some studies assessed intervertebral motion only in a few
segments (e.g. L3 to S1) [27, 32, 33, 42, 43] and some
others considered solely intersegmental angular displacement
without any attention to intersegmental linear translation
or other parameters, such as PICR [17, 34, 35, 44].
There are some studies which used camera to capture
images from monitor of analog fluoroscopy system [30,
In this improved study, flexion and extension movements
of lumbar spine were investigated in vivo by DVF.
In contrast to some previous studies, the image intensifier
of current study was not fixed while subjects wore a lead
harness which enabled us to measure intersegmental linear
and angular displacements at all vertebral levels within
whole range of motion and had better quality of digital
images. Furthermore, we used ICR and PICR variables to
identify the quality of motion and assessed neuromuscular
control of motion segments during lumbar movements
Our study indicated that arc length of PICR was significantly
different at L5 vertebra between two groups
through the extension movement of lumbar spine. Additionally,
independent sample t test was used for linear
translation excursion of L5–S1 segment to determine hypo
or hyper mobility in patients during flexion and extension.
These results showed no significant difference between two
groups. On the other hand, significant differences in the
midrange of this motion segment (Figs. 5, 6) indicated that,
however, linear translation of L5–S1 motion segment in
patients tended to extension, the total excursion of this
motion segment was similar to the healthy subjects. It
seems that the neuromuscular system adopts some
strategies to resist the anterior shear of the instable segment
in both extension and flexion movements. Therefore, these
results imply that the altered quality of movement in LSI
patients may be due to altered neuromuscular control. To
date, it is unclear that this alteration in neuromuscular
control is an adaptive mechanism to prevent further tissue
injury or the impairment of motor control system.
Another drawback in some previous studies is that the
segmental analysis was measured at certain fixed time
points or frame points [31, 32, 34, 35, 43, 44]. Since the
speed of lumbar movements and sagittal ROM of each
subject may be different, comparison of the results between
subjects becomes questionable. In this study, to control
variations across subjects in their sagittal ROM, each 25%
of total ROM was selected as a sampling point. We used
White and Panjabi method  for measuring intersegmental
linear translation and angular displacement because
Dupuis method of measurement  did not compute these
values for L5–S1 segment which ironically showed the
most significant differences in this study between the two
“Normal movement pattern” of lumbar spine during
flexion movement is not at as yet determined and there is
still some controversy in literature. Kanayama et al. 
concluded that each lumbar segment started stepwise from
the upper to the lower segment with a phase lag but Wong
et al. [34, 35] and Lee et al.  reported simultaneous
pattern for lumbar spine, while Okawa et al.  identified
both sequential and simultaneous pattern in normal
subjects. In this study we observed simultaneous movement
pattern in all healthy subjects and nine of the LSI
patients which imply that every lumbar segment does move
and in each time increment, each motion segment has a
specific contribution to the total lumbar movement.
It seems that hip fixation during the test may significantly
affect the quality of intersegmental movement patterns.
This concept has been warned against during functional
evaluation of spine (i.e. strength measurement) [46, 47].
Some previous studies fixed the hip to have better quality
of images [27, 31–33, 42, 43]; whereas, in this study the
subjects were free to move and we did not use any fixation.
Moreover, six patients showed sequential movement
pattern at the level of L5–S1 along with hypomobility in
the middle range of motion segment movement. In these
patients sequential pattern was accompanied with latency
which justified the term used as “Delayed-Sequence”
pattern. In these patients the impaired segment did not start
to move until 50% to 75% of total ROM had occurred. For
illustrative purposes, the linear translation and angular
displacement of one patient which showed delayedsequence
pattern is depicted in Figure 7.
It is known that patients with chronic LBP suffer from
episodic pain in their life [48, 49] and since the pain is a
confounding factor that may alter movement pattern of
lumbar spine [50, 51], researchers should consider the
severity of subjects’ pain. While previous fluoroscopybased
studies in this field did not consider this factor in
selecting their patients, we excluded patients with the pain
higher than 3 according to VAS during the assessment
session. Hence, in this study the effect of pain on movement
pattern was controlled.
Patients with LSI have been proposed as a unique subgroup
of LBP patients [36, 52–55] and LSI has been
defined as a condition in which there is a loss of stiffness of
spinal motion segments, such that normally tolerated
external loads result in pain . Diagnosis of LSI have
been developed traditionally from studies that have
examined intersegmental linear and angular displacement
using lateral flexion–extension radiographs and reported
some threshold values [6–19] but unfortunately their usefulness
is controversial. The use of these criteria for
identifying LSI has proven unsatisfactory because of high
false-positive rates [7, 12].
Schneider et al.  reported that patients with spondylolisthesis—
which demonstrate the hallmark of segmental
instability—showed reverse linear translation during lumbar
movement using functional radiography, while Teyhen
et al. indicated that patients with LSI showed hypomobility
in both flexion and extension movements  and reversed
intersegmental linear translation in the middle of flexion
movement using video fluoroscopy . The results of
current study imply that in both flexion and extension
movement arcs, through the middle of total lumbar range
of motion there were significant differences in the intersegmental
linear translation at level of L5–S1. Therefore,
our findings support that in presence of LSI the impaired
lumbar motion segment may not exactly follow the other
segments and show different behavior. Such abnormal
motions lead to abnormal loading of spine and may predispose
the discs to degeneration [58–61]. Multiple comparisons
were significant between all 5 phases of
movements at all motion segments because of the small
proportion of population of patients with delayed pattern.
In the current study subjects were asked to finish their
movement during 10–15 s. Upper bound of this time period
was for refraining from harmful radiation effects and lower
bound was because of limitation in sampling rate of fluoroscopy
system. Some previous related articles indicated
that there is no statistical difference between genders [34,
35, 44]. Future studies should once again use the current
protocol for evaluation of the gender effect on patterns of
movement. The other limitation in this study was
encountering with a nonhomogenous group of patients. Our
results imply that proposed screening criteria  were not
specific enough because nine patients showed similar
kinematics to healthy subjects. Much larger multicenter
studies are needed before we can develop more accurate
criteria for diagnosis of LSI patients groups.
It seems that with using devices, such as digital videofluoroscopy
which are capable of assessing kinematics of
lumbar motion segments in vivo, clinicians probably could
distinguish patients suspected to LSI. Therefore, in near
future by using these noninvasive techniques the patients
with LSI might be discriminated from other nonspecific
LBP, appropriate plan of treatment could be designed and
reassessment would be easier.
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